With power-OFF disconnect the HD. Now power-ON do you get the bios display or initial booting display. If so, then access the bios, verify the HD is the 1st device and save upon exit. if you get nothing, then something is wrong with mtrbd.. if you get a flashing cursor in upper left corner(maybe right) then it awaits proper initialization of system. return new HD to system and try again. HP maybe doing a check and it fails and won't allow to continue. In such cases it may need HP s/w to proceed. Only and only if the right recovery/restore discs were used, because HP has a tendency to make it go bad, otherwise.